Production examples
Backing Plates by FSW(Friction Stir Welding)
Advantage 1: Uniform Cooling Performance
In order to make the lid thickness uniform after the surface finishing process, as shown in the figure, a dedicated press machine is used to correct the warping and distortion of the base material and the lid. After that, the finishing process is carried out. A uniform lid thickness will be realized by this process. If the thickness of the lid is uniform, the distance from the groove (cooling channel) to the top surface of the lid (contact face) is also constant, and it has a cooling performance with no variation.
If the finishing process is done from the contact area without correction with a press machine, the thickness of the lid at the time of completion will change depending on the place as shown in the figure. If there is a thick part and a thin part of the lid with respect to the groove (cooling channel), a temperature difference will be created due to the difference in thickness, and as a result, the cooling performance will vary.
Advantage 2: High Joints Reliability
The joints by FSW can be made with the lid onto the base material closely without gaps.
In fusion welding by an electron beam that heats the material above the melting point temperature, there are concerns in the reliability of the joints due to slag and bubble. And in the brazing process, there are concerns about joint failure due to brazing shortage. On the other hand, FSW, which is a solid phase joining, is heated and softened as a solid without melting, and then pressurized to be joined. So there is almost no slags, air bubble and thus joining defects will rarely occur. Therefore, it has realized high reliability at the junction of the base material and the lid.
Advantage 3: High-Mix Low-Volume(HMLV) Production
The parts used in the manufacturing equipment in production line are different from the ones in mass-produced products, and equipment-specific customized ones are also required. Since FSW is used utilizing a dedicated processing equipment, it can be used for high-mix low-volume production.
Our processing equipment is a specially made hybrid machine that can perform cutting and joining (FSW) on the same machine. We have an integrated production system from machining to joining, and we can manufacture products that guarantee high quality.
Advantage 4: High Material Strength
FSW can maintain high material strength. In the case of brazing, the entire material will become hot during the brazing process and the base material will soften. In some cases, the more bend with own weight, the weaker the strength of the material becomes. On the other hand, FSW is a solid phase joining, and the base material does not soften because there is no need to heat the entire material. In addition, the joining part has a material strength equal to or greater than that of the base material. In this way, FSW is a joining method that does not reduce the material strength of the base material.
Things to consider when designing
1 Materials
Aluminum
The cost of aluminum is low that is about one-third of copper. The thermal conductivity shows a good value although it is about half compared to 236W · m-1 · k-1 and copper 398W · m-1 · k-1. On the other hand, Young’s modulus is about 70GPa, which is low and easy to deform compared to about 115GPa in copper and 196GPa in stainless steel. Therefore, if the usage environment with a relatively low load on the backing plate or if the heat generation is relatively low as low as copper, it can be produced at a low cost.
| Material |
Young’s modulus in ksi |
| C10100(OEE copper) |
16700 |
| C11000(ETP copper) |
16700 |
| C18200 Chromium copper |
18900 |
| Molybdenum |
47700 |
| 304 Stainless Steel |
28500 |
| 6061 Aluminium |
10000 |
*1ksi=6.8965517241379MPa
Copper
The copper backing plate using oxygen-free copper (C1020), which has the lowest oxygen content among pure copper is a mainstream. As for Tough- pitch copper materials, there are some concerns of generating gases in a vacuum environment. The thermal conductivity of copper has a high value of 398W · m-1 · k-1, and it is a relatively easy material to process. Copper materials are suitable for places where high heat dissipation is required or when complex processing is required. The Young’s modulus is also about 115GPa, which is high in strength and hard to deform. On the other hand, due to pure copper being a difficult-to-cut material, it is a material that requires high processing technology.
Stainless steel
Stainless steel has a thermal conductivity of 17W · m-1 · k-1 and that is not so good compared to copper but the Young’s modulus is 196GPa , which is higher than about 115GPa for copper.
On the other hand, it is not suitable for complex shapes and/or fine shapes due to poor processability.
2 Thermal Conductivity
During the sputtering process, the surface of the sputtering target will be hot, so the heat generated must be continued to be cooled. Therefore, backing plates are required to be made of materials with high thermal conductivity in order to efficiently cool the heat generated on the backing plate
In addition, if there is a temperature difference between the sputtering target and the backing plate, thermal stress will be generated, and cracks and peeling will occur with brittle materials, so it is also important to use materials with high thermal conductivity to equalize them.
Generally, thermal conductivity is material-specific, so if you want high cooling efficiency, a material with high thermal conductivity will be chosen.
3 Mechanical Strength
The backing plate also requires mechanical strength. There are two types of cooling methods for the backing plate in sputtering, a direct method to cool the backing plate itself and an indirect method that cools the device and cools it by heat conduction.
In the case of the direct method, high pressure is applied to the backing plate, which can cause the backing plate to warp and at the same time, warping, cracking and peeling of the sputtering target on the backing plate may occur.
Therefore, the backing plate requires a high strength (Young’s modulus) that is difficult to deform even if high pressure occurs. Since the Young’s modulus is material-specific, if you want to minimize the warping caused by cooling, you will choose a material with a high Young’s modulus.
